1. Field of the Invention
The present invention relates to an earth auger head and an excavation method using this earth auger head.
2. Description of the Related Art
In common earth auger heads, a spiral vane (screw) for discharging excavated earth is disposed on the tip part of a rotating shaft, and a bit used to excavate the ground is installed on the lower end part. The boring of holes is accomplished by the rotation of the abovementioned excavating bit (rotational excavation). In the hole boring excavation (rotational excavation) performed by the abovementioned earth auger head, when hard ground is struck during the excavation, the destruction of the ground by the excavating bit no longer proceeds. Accordingly, an excavating operation is again performed once the hard ground has been removed.
Furthermore, excavation means (percussive excavation) is known in which hole boring is performed by applying a strong shock to the ground and pulverizing the ground using an air pressure percussive excavation drill (down-the-hole hammer or the like) as means for handling hard ground excavation (Japanese Examined Patent Publication No. 7-91930). The above-mentioned percussive excavation is effective against hard ground, but the excavation efficiency is poor in the case of hole boring excavation performed on ordinary ground.
Accordingly, in order to incorporate the advantages of rotary excavation and percussive excavation, it has been proposed that an air pressure percussive type excavation drill (down-the-hole hammer or the like) be built into the earth auger head.
For example, in Japanese Registered Utility Model No. 3004848, Japanese Laid-Open Patent Application No. 9-177462, and Japanese Laid-Open Patent Application No. 10-159474, earth auger heads are disclosed in which the rotary shaft of the earth auger head is formed in a tubular shape, and a down-the-hole hammer is disposed inside this rotary tube.
Furthermore, in cases where a reinforced concrete block is formed by filling the excavated hole with a concrete block and inserting an iron reinforcing basket, the excavated hole is filled with a foot protection liquid such as cement milk or the like prior to the construction of this block.
The filling operation of this foot protection liquid requires the filling to be performed while the destruction of the excavated hole is prevented, and must therefore be performed while the earth auger is being withdrawn. Accordingly, in an earth auger head which is capable of performing both the abovementioned rotary excavation and the above-mentioned percussive excavation, both a high pressure air supply path and a liquid supply path are formed in the excavating rod as indicated in Japanese Examined Patent Publication No. 7-91930 and Japanese Registered Utility Model No. 3004848, a liquid jet opening is formed in the auger head, and successive filling with a foot protection liquid is performed from the bottom of the hole while the earth auger is withdrawn following the completion of excavation.
Furthermore, in Japanese Registered Utility Model No. 3004848, a switching valve mechanism which is switched by the weight of the auger head and the pushing in of the excavating rod is interposed between the excavating rod and the auger head, and the high pressure air supply path also acts as a liquid supply path.